Question

我已经创建了一个AsyncTask类来处理从我的服务器发送和接收。我正在尝试做的是在收到数据时触发事件或回调，这样我就可以使用所述数据来操作UI。

AsyncTask类：

public class DataCollectClass extends AsyncTask<Object, Void, JSONObject> {
    private JSONObject collected;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    //@Override -Commented out because it doesn't like the override
    protected void onPostExecute() {
        try {
            Log.d("Net", this.collected.getString("message"));
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected JSONObject doInBackground(Object... params) {
        OkHttpClient client = new OkHttpClient();

        // Get Parameters //
        String requestURI = (String) params[0];
        RequestBody formParameters = (RequestBody) params[1];
        Request request = new Request.Builder().url(requestURI).post(formParameters).build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                // DO something on FAIL
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                String jsonResponse = response.body().string();
                Log.d("Net", jsonResponse);
                try {
                    DataCollectClass.this.collected = new JSONObject(jsonResponse);
                    Log.d("Net", DataCollectClass.this.collected.getString("message"));
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        });

        return collected;
    }
}

这是有效的，它会将预期的JSON行打印到日志中。

它从Activity调用：

new DataCollectClass().execute(requestURI, formVars);

我看了一遍，似乎无法找到关于如何（以及在何处）添加回调的明确答案。优选地，回调代码本身应该与DataCollectClass一起使用，因此所有相关代码都可以在同一个地方重复使用。

有没有办法创建程序可以监听的自定义事件触发（类似于Javascript库）？

我一直把头发拉过来！

更新：

由于AsyncTask是多余的，我已将其删除并重写代码（以防其他人有同样的问题）：

public class DataCollectClass { 私有JSONObject收集;

    public interface OnDataCollectedCallback {
        void onDataCollected(JSONObject data);
    }

    private OnDataCollectedCallback mCallback;

    public DataCollectClass(OnDataCollectedCallback callback, String requestURI, RequestBody formParameters){
        mCallback = callback;
        this.collect(requestURI, formParameters);
    }

    public JSONObject collect(String requestURI, RequestBody formParameters) {
        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder().url(requestURI).post(formParameters).build();

        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                //TODO Add what happens when shit fucks up...
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                String jsonResponse = response.body().string();
                Log.d("Net", jsonResponse);
                try {
                    DataCollectClass.this.collected = new JSONObject(jsonResponse);

                    if(mCallback != null)
                        mCallback.onDataCollected(DataCollectClass.this.collected);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        });
        return collected;
    }
}

来自活动：

new DataCollectClass(new DataCollectClass.OnDataCollectedCallback() {
    @Override
    public void onDataCollected(JSONObject data) {
        if(data != null) {
            try {
                // Do Something //
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }
}, requestURI, formVars);

一切都完美！谢谢！

Answer 1

如果您想利用AsyncTask的回调，可以通过以下方式处理它。

执行类似的操作（修改代码以添加以下内容）

public class DataCollectClass extends AsyncTask<Object, Void, JSONObject> {

    public interface OnDataCollectedCallback{
        void onDataCollected(JSONObject data);
    }

    private OnDataCollectedCallback mCallback;

    public DataCollectClass(OnDataCollectedCallback callback){
        mCallback = callback;
    }

    // your code that is already there
    ...

    @Override
    public onPostExecute(JSONObject response){
        if(mCallback != null)
            mCallback.onDataCollected(response);
    }
}

然后让魔术发生

new DataCollectClass(new OnDataCollectedCallback() {
        @Override
        public void onDataCollected(JSONObject data) {
            if(data != null)
                // DO something with your data
        }
    }).execute(requestURI, formVars);

但值得注意的是，most networking libraries, including OkHttp, handle background threads internally, and include callbacks to utilize with the requests.

这也实现了一个自定义接口，因此其他人可能会看到如何将它用于任何AsyncTask。

Answer 2

有一个asynchronous get in OkHttp，所以你不需要AsyncTask，但作为一个学习练习，你可以将你的回调定义为一个类似的参数。

new DataCollectClass(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                // DO something on FAIL
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                JSONObject collected = null;
                String jsonResponse = response.body().string();
                Log.d("Callback - Net", jsonResponse);
                try {
                    collected = new JSONObject(jsonResponse);
                    Log.d("Callback - Net", collected.getString("message"));
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        }).execute(requestURI, formVars);

AsyncTask

public class DataCollectClass extends AsyncTask<Object, Void, Call> {
    private Callback mCallback;
    private OkHttpClient client;

    public DataCollectClass(Callback callback) {
        this.mCallback = callback;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        this.client = new OkHttpClient();
    }

    @Override 
    protected void onPostExecute(Call response) {
        if (response != null && this.mCallback != null) {
            response.enqueue(this.mCallback);
        }
    }

    @Override
    protected Call doInBackground(Object... params) {

        // Get Parameters //
        String requestURI = (String) params[0];
        RequestBody formParameters = (RequestBody) params[1];
        Request request = new Request.Builder().url(requestURI).post(formParameters).build();

        return client.newCall(request); // returns to onPostExecute
    }
}

Answer 3

使用asynctask调用Webservice是一种老式的。你可以使用Volley或改装。但是您可以使用此过程来调用Webservice。以下是步骤：

创建一个接口并在您的Activity / Fragment

中实现它

public interface IAsynchronousTask {
        public void showProgressBar();
        public void hideProgressBar();
        public Object doInBackground();
        public void processDataAfterDownload(Object data);
 }

创建班级DownloadableAsyncTask。这堂课是：

import android.os.AsyncTask;
import android.util.Log;

public class DownloadableAsyncTask extends AsyncTask<Void, Void, Object> {

    IAsynchronousTask asynchronousTask;

    public DownloadableAsyncTask(IAsynchronousTask activity) {
        this.asynchronousTask = activity;
    }

    @Override
    protected void onPreExecute() {
        if (asynchronousTask != null)
            asynchronousTask.showProgressBar();
    }

    @Override
    protected Object doInBackground(Void... params) {
        try {
            if (asynchronousTask != null) {
                return asynchronousTask.doInBackground();
            }
        } catch (Exception ex) {
            Log.d("BSS", ex.getMessage()==null?"":ex.getMessage());
        }
        return null;
    }

    @Override
    protected void onPostExecute(Object result) {
        if (asynchronousTask != null) {
            asynchronousTask.hideProgressBar();
            asynchronousTask.processDataAfterDownload(result);
        }
    }

}

现在，在您的活动中，您将找到此方法。

DownloadableAsyncTask downloadAsyncTask;
ProgressDialog dialog;
    private void loadInformation() {
            if (downloadAsyncTask != null)
                downloadAsyncTask.cancel(true);
            downloadAsyncTask = new DownloadableAsyncTask(this);
            downloadAsyncTask.execute();

        }

        @Override
        public void showProgressBar() {
            dialog = new ProgressDialog(this, ProgressDialog.THEME_HOLO_LIGHT);
            dialog.setMessage(" Plaese wait...");
            dialog.setCancelable(false);
            dialog.show();

        }

        @Override
        public void hideProgressBar() {
            dialog.dismiss();

        }

        @Override
        public Object doInBackground() {
            // Call your Web service and return value

        }

        @Override
        public void processDataAfterDownload(Object data) {
            if (data != null) {
                // data is here
            }else{
                //"Internal Server Error!!!"
            }

        }

现在只需拨打loadInformation()方法，您就会在processDataAfterDownload()上收到回复。

使用AsyncTask创建回调函数

3 个答案: